Portable electronic devices, such as mobile phones or any hand-held computer in general need a regulated voltage even from an unregulated voltage source, for example a battery. For generating and maintaining for a predetermined operation period the required regulated voltage, a voltage regulator is used. The voltage regulator is often provided in the form of a DC/DC-converter which is operated by a power source, such as the battery and generates a DC output voltage. The output voltage may be produced at a higher or lower value than the input voltage according to the voltage to be used for supplying power to the mobile devices. For obtaining an output voltage that is higher than the input voltage, a so-called boost or step-up converter is utilized, and for obtaining a lower voltage level, a so-called buck or step-down converter is used.
Since the voltage provided by a battery may vary in a relative broad range from a fully charged status to a partly or completely discharged status, the voltage regulator is also required to provide a certain output voltage from a range of input voltages which may comprise higher and lower voltages as the specific input voltage of the DC/DC-converter.
The implementation of a voltage regulator, such as a DC/DC-converter is in general a switching regulator and includes a circuit that uses an energy-storage element, such as an inductor or coil, to transfer energy from the unregulated power source having a higher or lower voltage than desired, such as a battery with varying state of charge, and the temporarily stored energy is transmitted in discrete pulses to a load. In case a feedback circuitry is provided the energy transfer process can be set to a predetermined value and can be controlled for maintaining a basically constant output voltage at the load connected to the voltage converter.
In case the DC power source is in such a manner unregulated that the input voltage of the DC/DC-converter may be lower or higher than the desired output voltage, probably due to the considerably varying state of charge of the battery and, thus, of the output voltage thereof, an up and down converter (buck-boost) converter is required to provide a regulated output voltage from such a kind of source by regulating the output voltage to the predefined level depending upon the properties of the load connected thereto. The up-down converter provides a regulated output voltage over large variations of the unregulated voltage source providing the input voltage thereof, and control is needed to obtain desired output voltage results.
Reference United States 2005/0218876 A1 discloses a reversible buck-boost chopper circuit, wherein rectifier elements are provided in a first half-bridge circuit and a second half-bridge circuit. The first half-bridge circuit is connected to the power supply side and is also connected to an inductor forming the energy storage device. The second half-bridge circuit is connected to the inductor and to the output side of the chopper circuit to which the load is connected. Each of the first and second half-bridges includes semiconductor switching elements provided in the form of field effect transistors, and a central controller generates drive signals for controlling the switching status of the semiconductor switching elements of both half-bridges. The controller can provide drive signals to turn on and off at least one of the plural semiconductor switches of both half-bridges to obtain different output voltages. A first output voltage is applied to the high-side terminal of the load, and a second output voltage is applied to the low-side terminal of the load, thereby operating the load based on a differential voltage between the first and the second output voltages. The differential voltage defines a predetermined DC output voltage for the load. A current sensor is provided for sensing the current from the power source to the chopper circuit, and a voltage sensor is provided for sensing the output voltage of the chopper circuit applied to the load. This allows a current-feedback control and a voltage-feedback control so that over-current conditions are avoided and the load can be provided with a desired voltage level for operation. The chopper type DC/DC-converter has a reversible power-transmission capability and allows a voltage applied to the load to be generated by step-up or step-down process with respect to the DC voltage of the DC power source, based on the feedback control of the operational parameters.
Furthermore, FIG. 1 shows a basic arrangement of a DC/DC-converter or voltage converter 100 including an automatic up/down converting function for obtaining the required DC output voltage Vout for driving a load LD based on a DC input voltage Vin, probably taken from a power supply PS such as a battery connectable to the voltage converter 100. The voltage converter 100 is arranged to transfer electrical energy from the power supply PS which constitutes an unregulated voltage source having the voltage Vin at the terminal IN to a corresponding output voltage Vout to be supplied to a load LD connectable to the voltage converter 100. That is, the DC/DC-converter 100 is adapted for carrying out an automatic up/down mode and provides the regulated output voltage Vout for the load LD by switchable current paths including an inductive element L. A plurality of switching elements S1 to S4 is provided for switching the current paths of the voltage converter as a forward-phase current path when the input voltage corresponds to the output voltage, an up-phase current path when the input voltage is lower than the output voltage, and a down-phase current path when the input voltage is higher than the output voltage.
The voltage converter 100 includes in particular a first switching element S1, a second switching element S2, a third switching element S3 and a fourth switching element S4. The switching elements S1 to S4 may be provided in the form of field effect transistors and may specifically be implemented by using PMOST and NMOST power transistors. The present voltage converter 100 in the arrangement shown in FIG. 1 provides the automatic up/down conversion function by combining an up converter with a down converter using a single inductance element or inductor L (coil).
The single inductor L is connected in series to the first switching element S1. Between a common node of the first switching element S1 and the inductor L and the ground potential GND, the second switching element S2 is arranged. At the other node NB of the inductor L the third switching element S3 is connected between this node and ground potential GND, and the fourth switching element S4 is connected between this node NB and a capacitor C. The capacitor C is connected in parallel to the output terminals of the voltage converter 100 between the output voltage Vout and ground potential GND.
The voltage converter 100 further comprises a digital control circuitry CCU (central control unit) which provides control of the conversion operation of the voltage converter, and the digital control circuitry is in particular adapted for controlling the switching status (open or closed state) of the respective switching elements S1 to S4.
In general, voltage converters are current mode converters, which means that the current through the inductor L is sensed and switched to a different state when a peak of the current is reached.
Regarding the operation of the voltage converter 100 shown in FIG. 1, by selectively maintaining or changing the switching status of particular ones of the plurality of the switching elements S1 to S4 different current paths can be defined including the inductor (coil) L.
When the input voltage Vin which corresponds to a battery voltage Vbat when the voltage converter 100 is connected to a battery (not shown), is higher than the desired output voltage Vout (Vbat>Vout), then the fourth switch S4 is always closed and the first and second switches S1 and S2 are alternately switched on (that is, they are alternately switched to the conductive state). The current through the first switching element S1 is sensed representing the current through the inductor L, and when the current through the first switching element S1 reaches a peak, the first switching element S1 is switched off and the second switching element S2 is switched on and starts to conduct. This corresponds to the down mode for generating an output voltage Vout which is lower than the input voltage Vin (exhibiting the function of a buck converter).
In the up mode, that is, when the input voltage Vin which corresponds to the battery voltage Vbat is smaller than the desired output voltage Vout (Vin>Vout), the first switching element S1 is always closed (conductive), and switching is in a controlled manner performed between the third switching element S3 and the fourth switching element S4. In this mode, the third switching element S3 is the active switch, and the fourth switch S4 could be replaced with a passive diode. In this case, the current through the third switching element S3 is sensed, and the third switching element S3 is switched off, when a predetermined peak current is reached. The predetermined peak current may constitute a program peak current.
As mentioned above, depending upon the operation of the voltage converter, currents through the first switching element S1 and the third switching element S3 are sensed. Accordingly, a matching of the sensing of the current values is necessary for obtaining reliable current values for an optimized control of the voltage converter 100. Moreover, this measurement concept requires a certain circuitry rendering the circuit arrangement of the voltage converter 100 complicated.